Duplicando objetos!

EntityManagerFactory emf = Persistence.createEntityManagerFactory("pontoPU");

        EntityManager em = emf.createEntityManager();
        EntityTransaction tx = null;
        try{
            tx = em.getTransaction();
            tx.begin();
            Usuario u = new Usuario();
            u.setLogin("mrsmylle");
            u.setSenha("123456");
            em.persist(u);
            em.flush();
           tx.commit();
        System.out.println("Persistido!!");
        }catch(RuntimeException e){
            e.printStackTrace();
        }finally{
            em.close();
           
        }